I´ve photographed a lot of sunsets this year. Downloaded LR4 yesterday and imported LR3 catalogs. When switching to the new "2012 engine" the colors are not the same, have to adjust orange hue + 15-30. Think the LR3 version is more accurate.

For these pictures I´ve used Pansonic FZ35 raw files converted to dng when imported to LR3. Have not made any adjustments in the HSL panel in LR3.

Maybe a new color profile is used i LR4, other camera profiles may also have been changed ...

There's no sense of "accuracy" when it comes to raw conversion, so I don't think it's correct to call this an issue. The color reproduction of the new process is quite a bit different than P2010, and can be a little jarring if you're doing a switch. It's important to remember the "zero" values in Lr are just arbitrary starting points. They very well could have made it so all the sliders start at -100 and you need to start working from there. Obviously every photo would look bad to begin with, and it would be the user's job to find good values for all the settings. Think of this the same way, even though 2012 looks way too low in orange, that's just a starting point; it's not really a "problem" that you need to go to +30.

If the images you're working on have any previous adjustments (you say no HSL adj, but don't mention anything else), likely some combination of what you already have in there just interacts with P2012 very differently than P2010. Camera profile is the most likely candidate, since some of those have very dramatic effects on the color primitives, which all other settings are based on.

I would suggest (for science), making a virtual copy and resetting it, then re-developing the photo as though you had never done it before. Re-make all the decisions. I suspect if you select profile, set exposure, vibrance, etc you will get to HSL without needing to rack orange that far.

All that being said, unless you have a need to, switching processes isn't really something you should do by default. The switch to P2010 had a lot more to do with noise and sharpness rather than color, so a lot of the time people could get away with doing the switch in bulk, but that's not the case with 2012.

To make a bad analogy, it's kind of like starting with a song, say the Star Spangled banner, as your "raw data". The difference between P2010 and P2012 is the difference between the Boston Symphony and Jimi Hendrix playing it. It's the same song, same notes on the sheet music, but being interpreted in very different ways. If you've already heard the song one way and that's the way you like it, you shouldn't expect to be able to switch and get the same result. Not to say the other way is bad, but it will be different. It may be the case, like songs, that you want both, but they're never going to be the same.